1. Field of the Invention
The present invention relates to a cantilever type probe used in a scanning tunnel microscope (STM) and an information recording and reproducing apparatus utilizing the principle of scanning tunneling microscopy.
The present invention also relates to a scanning tunnel microscope and an information processing apparatus which can perform recording, reproducing and erasing of information.
2. Related Background Art
Recently, there has been developed a scanning tunnel microscope with a resolving power on the atomic or molecular order. The concept of STM has been applied to analyze surface structures and to measure surface roughness and the like.
The scanning tunnel microscope (hereinafter abbreviated as STM) is based on the phenomenon that tunnel current changes exponentially dependent upon the distance between a conductive probe and a conductive specimen when they are made to approach each other at a distance of about 1 nm with a voltage applied therebetween.
An image of the surface of a specimen can be obtained utilizing the change of tunnel current caused by the atomic arrangement or uneven structure of the surface of the specimen when a probe, which has a very sharp tip formed by electrolytic polishing and the like, is scanned two-dimensionally while keeping the distance between the probe and the surface of the specimen, which comprises conductive material, constant [G. Binnig et al., Phys. Rev. Lett. Vol 49 (1982) 57]. Moreover, there has been proposed an apparatus capable of high density recording and reproduction by utilizing the principle of STM and a medium which has a surface having a fine, uneven structure or with electrically different portions.
In such an apparatus, it is necessary to scan the specimen using a probe in a range of several nm to several .mu.m. A piezoelectric element is used as a moving mechanism. As examples of such a moving mechanism, there are the tripod type and the cylindrical type. The Tripod type mechanism is one which combines three piezoelectric elements which are perpendicular to each another along the x, y and z directions and a probe which is located on the intersecting point of the three elements.
A cylindrical type mechanism utilizes one end having divided electrodes provided around the peripheral surface of a cylindrical piezoelectric element. A probe is provided on the other end of the divided electrodes which is able to scan, which makes the cylinder bend corresponding to each divided electrode.
Lately, attempts have been made to form a fine cantilever type probe by employing micromechanical techniques utilizing semiconductor processing.
FIG. 12 shows an example of a prior art piezoelectric bimorph cantilever formed on a silicon (Si) substrate by employing a micromechanical technique in accordance with the Proceedings of 4th International Conference on STM/STS, page 317.
FIG. 12(a) is a perspective view of such a cantilever.
The cantilever is formed on a silicon substrate by laminating divided electrodes 4a and 4b, ZnO piezoelectric material 5, common electrode 3, ZnO piezoelectric material 5 and divided electrodes 2a and 2b in this order, followed by removing a part of the silicon substrate under the cantilever by anisotropic etching.
The metal probe 7, which is provided on one end of the piezoelectric bimorph cantilever by adhering or the like, can detect tunnel current through a drawing electrode 6.
FIG. 12(b) is a sectional view of the cantilever. The cantilever can be moved three-dimensionally and independently by controlling voltages applied on four regions of piezoelectric material which comprise two regions sandwiched between upper divided electrodes 2a and 2b and common electrode 3 and two regions sandwiched between lower divided electrodes 4a, 4b and common electrode 3.
FIG. 13 (a), (b) and (c) are illustrations showing motions of a prior art cantilever in driving by changing combinations of regions to which voltages are applied within four regions of piezoelectric material divided by pair of divided electrodes.
FIG. 13(a) shows the motion of a cantilever which can move probe 7 toward the y-direction shown in FIG. 12(a) when voltages with the same phase are applied so that four regions can contract simultaneously. FIG. 13(b) shows the motion of a cantilever which can move probe 7 toward the x-direction shown in FIG. 12(a) when an upper and lower region in the right side in FIG. 13(b) stretch and an upper and a lower region in the left side contract. FIG. 13(c) shows the motion of cantilever which can move probe 7 toward the z-direction shown in FIG. 12(a) when a right and a left region in the upper side contract and a right and a left region in the lower side stretch.
In the prior art, however, there has been a problem in that noises by control voltage are induced in probe 7 and drawing electrode 6, because the drawing electrode 6 for probe 7 is placed adjacent to the driving electrodes of the piezoelectric bimorph. Accordingly, noises are overlapped on the fine tunnel current detected, which makes it difficult to obtain precise STM images.
Moreover, in the prior art, there has been a problem that probe 7 runs into a sample surface and the probe is damaged because a feedback control to maintain the distance between the probe and sample is subject to such overlapping noises.